Arrangement for producing a series of pulses



June 5; 1962 E. F. HENZE ARRANGEMENT FOR PRODUCING A SERIES OF PULSES Filed Feb. 7, 1958 2 Sheets-Sheet 1 June 5, 1962 3,038,028

E. F. HENZE ARRANGEMENT FOR PRODUCING A SERIES OF PULSES Filed Feb. '7, 1958 2 Sheets-Sheet 2 r L T I I %L I United. States Patent 3,038,028 ARRANGEMENT FOR PRODUCING A SERIES OF PULSES Ernst F. Henze, Ulm (Danube), Germany, assignor to Telefunken G.m.b.H., Berlin, Germany Filed Feb. 7, 1958, Ser. No. 713,933 Claims priority, application Germany Feb. 26, 1957 Claims. (Cl. 178-22) It is well known that a text to be enciphered, which consists of a series of characters, telegraphic signals, teleprinter marks, coded language or coded picture contents, can always be considered as a series of figures to be enciphered. It has also been known for a long time to encipher such texts by using methods which consist in adding to the text in clear a substantially random series of such signals or marks which, as aforementioned, can be considered as figures. It has also been proposed to represent such a series of figures in dual figures in order to add it to the dually coded text in clear. A secret text so produced may then be deciphered by subtracting the series of figures employed.

In most practical cases it is now desirable to use as an enciphering text a series of figures which can be reproduced at any time without its having tobe recorded on a perforated tape or the like. It is then no longer necessary to forward any secret material to the receiving end, whereas previously the enciphering text had to be sent, for example, on a perforated tape to the information receiver. But reproducible enciphering cannot obviously be wholly random; it has to be built up according to predetermined rules. But in view of enciphering safety, a reproducible enciphering text can be just as good as a wholly random one when the generation process of the pulse series used as an enciphering text is of such a type that it allows for no recognition of generation rules, for example initial setting of the generating apparatus.

An object of the invention is to provide an arrangement for generating a series of n-position, binary enciphering figures for enciphering signals which appear in binary form.

A further object of the invention is to apply such an arrangement to encipher teleprinter signals or quantized,

binary-coded audio signals while using the normal transmission equipment, which means maintaining the bandwidth of the signal 'even for the enciphered signal.

A further object of the invention is to provide such an enciphering arrangement which is as safe as possible against any unauthorized deciphering even when the apparatus itself or at least its design is known by an unauthorized person. Under such conditions a sufficient safety will only be ensured if, in the first place, enciphering is not stable but varies continuously and, in the second place, if the enciphering period which in all cases is present lasts so long that practically it can not be recognized.

A still further object of the invention is to provide a ciphering machine which allows for a very great number of possible enciphering settings (of the order of magnitude of about According to the enciphering method of the invention foreign binary elements (so-called enciphering elements) are added to the information elements existing in binary form and are subtracted when deciphering.

For speech enciphering for which the arrangement according to the invention is preferably used. it is thus necessary in first place to provide an additional device which converts the speech currents of a telephone channel into a binary form, the bandwidth of the so coded speech being not greater than that of a telephone channel, that is, about 3 kcs. As known, the human voice has so great a redundancy that when compressing the speech band to about 600 cs. syllable intelligibility is still sufficient while the voice character is maintained. In order to accurately transmit information contained in a 600 cs. wide band it is sufiicient to sample the signal amplitude 1200 times a second and to transmit these 1200 amplitude samples per second. The amplitudes of said samples will be sufficiently correct if they are transmitted by thirty-two different amplitude levels, so that each amplitude sample can be represented as a five-position binary number. Thereby a signal of 5.1200=6000 bits/sec. is obtained, allowing for transmission in a 3 kcs. wide frequency band, as requested above.

The aforementioned coding process of an audio band does not constitute the object of the invention but serves only to explain the possibility of translating audio information transmitted in a 3 kcs. wide telephone band into the form of a binary code whose transmission requires the same bandwidth. It will be appreciated that there are also many other speech coding possibilities.

According to the invention the arrangement for generating a series of n-position, binary enciphering numbers comprises m counters having different aliquant period lengths, an n-position enciphering store and a switching device for connecting the m counter outputs to the n encipheringlstore inputs via gate circuits.

According to another embodiment of the invention there is provided an arrangement for enciphering binary signals which comprises'an adding device for n-position binary numbers, said device delivering the enciphered signals and being supplied on the one hand with signals in groups of n binary steps which appear as n-position binary numbers and on the other hand with the n-position enciphering numbers obtained from the enciphering store. Means are provided to cause the enciphering generator to produce a new n-position enciphering number after each nth signal step and to feed it to the enciphering store. As aforementioned, the enciphering generator comprises mcounters, e.g. ring counters, having different, aliquant period lengths which after each nth signal step are simultaneously switched on one step further and whose outputs are coupled to respective n-poled switches via gates, the n poles of each switch being coupled to the n input terminals of the enciphering store. V

The enciphering storeitself can be constructed as an nstage ring counter, the input terminals of the n stages of the ring counter forming the n input terminals of the enciphering store and the output terminals of the n stages of the ring counter forming the n output terminals of said store. Preferably the adding device comprises n binary adding stages without any carry over, so that addition in each stage is performed modulo 2.

FIG. 1 shows the application of the invention to an arrangement for secret enciphering of quantized, binarycoded speech signals.

FIG. 2 shows the application of the invention to secret enciphering of teleprinter signals.

In the arrangement according to FIG. 1 the binaryvcoded speech signal is fed to the input terminals EK and transformed into pulses of the relay ER. From the relay contact er said pulses are applied to the oscillator O for synchronisation purpose, thus tuning said oscillator to the frequency of the incoming binary signals. Furthermore the relay pulses are fed via the conductor EL to a number of gates T and form the signal input of the adding device AW. The oscillations of the oscillator 0 control a distributor V comprising a five-stage ring counter consisting for example of five flip-flop stages connected in a ring. The five stages of the distributor V deliver five pulses successively through which the gates at, b, c, d, e of T are successively rendered conducting, so that the first five binary steps of the input signal are applied to the adding stages a, b, c, a, e respectively of the adding device AW. Via delay members 1' the gate pulses of as illustrated in the drawingor switches; altogether there are 51:120 different possible combinations; After the addition process in the adding device AW the latter is read out and'erased. This is done by means of a number of read out tubes AA, which are controlled by the distributor via delay members T The delay time 7'2 must be longer than the delay time 1-; so that each stage a, b,.c, d, e of the adding device AW is read out only after the respective signal step and enciphering step have been added. The read out pulse causes the sum value v or 1 contained in each stage of the adding device to be transferred to p the output conductor AL and erased in the adding device at the same time. Therefore, the five enciphered signal steps appear in the output conductor successively and actuate the output relay AR, whose contact ar feeds the output signal to the output terminals AK. 7

A new encipheringnumber is produced after each fifth step of the distributor V. This is initiated via the conductor SL which leads from the unite of the distributor to the enciphering generator SE. Said generator comprises a number m=l0 of ring counters Z Z having different period lengths. To avoid enciphering sub-periods, aliquant counting periods must be selected for the various ring counters. For the sake of simplicity, the first ten prime numbersfrom 2 are selected, namely: 2, 3, 5, 7, 11,13, 17, 19, 23 and 29. These numbers, which are only given by way of example, are indicated for clearness on the drawing after the corresponding references Z etc. of the ring counters. Each pulse coming through the conductor SL causes each ring counter to step up by one position. Under such conditions, the counter Z delivers an output pulse after every second oncoming pulse, the counter Z after every third, the counter Z after every fifith and so on, the counter 10, after every twenty-ninth oncoming pulse. Said output pulses are distributed via ten gates T and ten corresponding five-pole switches S S to the five flip-flop circuits 1, 2, 3, 4, 5 of the enciphering store SS. Owing to diiferent adjustments of the switches S S there exist 5 =9,765,62 5 different possibilities for feeding the enciphering store.

Now, care must .be taken in order that the gates 1 10 of the gates means T should not become conducting simultaneously, but successively, in such a manner that at any time, in a period of five bits, all the ring counters Z Z are connected successively to the corresponding flip-flop circuits of the enciphering store SS. For this purpose, there is provided a drequency doubler FV which doubles the frequency of the oscillator. This doubled output frequency from FV is applied via a delay member 1- to,the input of the enciphering read out circuit SA. During five binary steps this read out circuit thus receives ten step-up pulses which are so fed successively tothe ten flip-flop stages 1 10- of said circuit that they cause the corresponding gates 1 10 of the gating tmeans T to conduct successively, and the contents, of the corresponding ring counter units Z Z to be transmitted successively to the enciphering store.

The arrangement such as previously described for enciphering a binary information text can also be used ,for deciphering without any modification. Since the adding device adds modulo 2 in its various stages a, b, c, d, e, the enciphered text will be simply deciphered through repeated addition of the enciphering text, as it is well known that 1+l=0 (mod. 2) and 0+0=0 (mod. 2).

stages in the adding device, since the enciphering genera I It will also be appreciated that in the aforedescribed process a synchronisation between information transmitter and information receiver is only necessary in so far as the starting point of the enciphering or deciphering process must be marked; for this purpose the enciphering generator must obviously start fromthesarne initial position in both cases. Consequently, the invention can also be applied to radio-telephony trafiic between two stations if both enciphering generators of said. two stations are starting simultaneously from the same initial positions and, of course, if the positions of the; switches S S and the plugconnections between I, II V and A, B E are identical. With less severe requirements on the length ofthe. enciphering period, one can do with a smaller number m of ring counters in the en ciphering generator. In any case, it is advantageous to make the number of ring counters equal to an integral multiple (including unity) of. the number of the adding tor can then be synchronised by an integral multiple of the oscillator frequency.

The afore-described arrangement enables a very large number of enciphering modes N to be obtained. If the number of possiblestarting positions of the enciphering generator is denoted by N1 Nl=2.3.5.7 29-6.5.1O

the number of possible plug connections between the jacks I, II VandthejacksA,B EbyNZ the number of output positions of the enciphering store and the number of different switch positions S S S10 N4=51R19.8.10B there results for N The enciphering period, i.e. the number of steps after which the cycle of the enciphering generator is repeated, is equal to the number P=N 1:65.10 bits. This corresponds, in the case of a compressed audio band of 600 cs. wherein 6000 bits/sec. occur, to a period of T-300hours, which means a sufiiciently long period to make any recognition thereof impossible.

FIG. 2 illustrates diagrammatically a modification of the ciphering arrangement according to FIG. 1 for enciphering teleprinter signals. In teleprint, each character consists of a combination of five successive binary digits, preceded however by a start pulse and ended by a stop pulse. Consequently, the arrangement according to the invention will only be used for the actual code signals, while start and stop pulses are not enciphered and will so unenciphcred be applied to the output.

In FIG. .2 the identical elements are denoted by the same reference numerals as in FIG. 1 and the unchanged connections between the various parts are only indicated where they are necessary for understanding the modification relating to teleprinter enciphering. To the elements already described with reference to FIG. 1 there is added at the input a switch box SW which switches on the oscillator O on the occurrence of every start pulse and cuts it off on the occurrence of every stop pulse. In this manner the distributor V is controlled by the oscillator 0 only by means of the actual code signals representing the various characters among which each group of five are disposed between a start pulse and a stop pulse. The enciphering generator can step up as shown in the drawing under the direct action of the switch box SW, for example after each start pulse, so that the conductor SL is no longer connected to the distributor V as in FIG. 1 but to the switch box SW.

Since the start and stop pulses must be added to the enciphering signal the read out unit AA is completed by two further control tubes which are denoted in the drawing by start and stop and are connected to the switch box SW via corresponding delay members 1- and r Delay times T4 and 1- are so calculated that the start and stop pulses are inserted at the right moments into the enciphered signal coming from the adding device AW.

For enciphering teleprinter signals the oscillator O is tuned to a correspondingly lower frequency, say 50 cs., than for enciphering speech signals, so that the whole enciphering process is being carried out at the standardized teleprint transmission speed.

I claim:

1. An arrangement for secret enciphering an n-digit binary number made up of signals which appear in binary form, said arrangement comprising: an enciphering generator having m counters of difierent aliquant period lengths, each counter being a means for generating an output signal only at the end of the period of the respective counter; means for stepping said counters in sequence one step whenever the incoming signals have made up an n-digit binary number; an n-position enciphering store having n inputs and n outputs; a switch-over device having m. inputs and n outputs arranged to form means for connecting any of the m counter outputs to any of the n store inputs; means for adding the contents of said store to the n-digit binary number to be enciphered; and selective interconnection means for selectively connecting any output from said store to an input of said adding means.

2. An arrangement according to claim t1 wherein the enciphering store comprises an n-position ring counter the input terminals of which form the n input terminals of said store and the output terminals of which form the 11 output terminals of said store.

3. An arrangement according to claim 1 wherein the adding means consists of n binary adding stages without any carry over so that in each stage addition is performed modulo 2.

4. An arrangement according to claim 1 wherein the number m is selected as equal to a multiple, including unity, of the number n, and further comprising oscillator means connected to said enciphering generator for direct- UNITED STATES PATENTS 2,403,888 Cronburg July 9, 1946 2,406,032 Parker Aug. 20, 1946 2,406,046 Swezey Aug. 20, 1946 2,794,851 Morris June 4, 1957 

